Check return value of GetStringPiece for (optional) kCCRT/kCCS in

net/quic/crypto/quic_crypto_server_config.cc

Index: net/quic/crypto/quic_crypto_server_config.cc
diff --git a/net/quic/crypto/quic_crypto_server_config.cc b/net/quic/crypto/quic_crypto_server_config.cc
index 2e804df96a620abd88027ab40e8937304c5a82a3..bfd3ed34982a946a174c0c2bf07ad4452119faf6 100644
--- a/net/quic/crypto/quic_crypto_server_config.cc
+++ b/net/quic/crypto/quic_crypto_server_config.cc
@@ -1139,12 +1139,14 @@ void QuicCryptoServerConfig::BuildRejection(
   }
 
   StringPiece client_common_set_hashes;
-  client_hello.GetStringPiece(kCCS, &client_common_set_hashes);
-  params->client_common_set_hashes = client_common_set_hashes.as_string();
+  if (client_hello.GetStringPiece(kCCS, &client_common_set_hashes)) {
+    params->client_common_set_hashes = client_common_set_hashes.as_string();
+  }
 
   StringPiece client_cached_cert_hashes;
-  client_hello.GetStringPiece(kCCRT, &client_cached_cert_hashes);
-  params->client_cached_cert_hashes = client_cached_cert_hashes.as_string();
+  if (client_hello.GetStringPiece(kCCRT, &client_cached_cert_hashes)) {
+    params->client_cached_cert_hashes = client_cached_cert_hashes.as_string();
+  }
 
   const string compressed = CertCompressor::CompressChain(
       *certs, params->client_common_set_hashes,